The invention relates to a bearing disk construction for supporting a spinning rotor shaft of an open-end spinning unit of the type disclosed in said co-pending application. To the extent necessary for an understanding of the present invention, the contents of this pending application are incorporated herein by reference thereto. U.S. Pat. No. 3,779,620 also relates to a bearing assembly of the type with which the bearing disk constructions of the present invention could be utilized.
The above-mentioned pending application and U.S. Pat. No. 3,779,620 suggest the use of two pairs of supporting disks forming a wedge-shaped gap for supporting from underneath the spinning rotor shaft, the rotor shaft being held and pushed against the supporting disks by a driving belt. In the above noted co-pending application, these supporting disks are formed with a metallic disk-shaped base body having a plastic ring fitting circumferentially surrounding same for engaging the spinning rotor shaft. This co-pending application suggests providing that the running surfaces of at least the supporting disks of the pair facing or closest to the rotor be arranged with a circumferential ring groove in order to avoid that the running or bearing surfaces are heated with an increased rotational speed in an inadmissible manner.
The present invention is particularly concerned with providing an improved practical construction of the bearing arrangements, and especially the supporting disks themselves for use in bearing arrangements of the above-mentioned type. Preferred embodiments of the supporting disk construction in accordance with the present invention are constructed with a metallic disk-shaped base body surrounded by a plastic fitting ring, the plastic ring forming the bearing support or running surfaces for the rotor shaft. According to an especially advantageous feature of the present invention, the plastic fitting ring is anchored in a circumferential groove provided in the metallic base body. This arrangement facilitates the ease of manufacture and assures a reliable retention of the plastic fitting ring at the metallic base body.
According to certain preferred embodiments of the invention, the plastic fitting ring includes a circumferential outer ring groove of a specific configuration for minimizing heat build up during use of the bearing disk. In order to minimize the heat build up while at the same time providing for a good running surface for the rotor shaft, it has been determined according to the invention that the following geometric relationships between the plastic fitting ring and groove are advantageous:
(i) the width of the groove in the axial direction of the disk is between one-sixth (1/6) and one-twelfth (1/12) of the total axial width of the plastic fitting ring;
(ii) the radial depth of the groove is approximately one-half of the total radial thickness of the fitting ring; and
(iii) the groove is disposed in the axial middle of the fitting ring.
In especially preferred embodiments, the plastic fitting ring has chamfered or bevelled edges at the inlet to the ring groove at both sides, which bevelled edges extend at an angle slightly less than 45.degree. with respect to the radius of the disk and to a depth of about one-third (1/3) the radial depth of the groove. Bevelled edges are also preferably provided at the axial end faces of the fitting ring. This bevelled edge construction minimizes stress areas and accommodates a smooth running relationship between the fitting ring and the rotor shaft supported thereon. In especially preferred embodiments, these bevelled edges and the rotor shaft support surfaces of the plastic fitting ring are smoothly polished.
According to especially preferred embodiments of the invention, the plastic fitting ring is formed of the material Simritan x 95 AU 19 785, a polyurethane, manufactured by the firm Freudenberg in Germany, which material exhibits a hardness of 52 Shore D.
In especially advantageous arrangements of the supporting disk, the metallic base body includes an annular cut-out between a hub portion for accommodating the support axle for the disk and a rim portion for supporting the plastic fitting ring. This construction further minimizes the weight and energy dissipating resistive moment of the bearing arrangement, while retaining the necessary support for the axle and for the plastic fitting ring which engages the rotor support shaft.
Preferred embodiments of the invention contemplate that at least the pair of support disks closest to the rotor are provided with the heat minimizing ring groove at the plastic ring fitting. However, especially preferred embodiments of the invention contemplate the provision of such ring grooves in all four of the supporting disks.
The construction of the disks according to the present invention is especially advantageous for use with modern high rotational speed rotor spinning machinery where rotor speeds in excess of 80,000 revolutions per minute (rpm) are contemplated. Not only does the arrangement of the combination metallic disk body and plastic ring fitting minimize the weight and energy requirements of the supporting disks while retaining the structural integrity to withstand the high forces exerted by the driving of the rotors during use, the disk construction of the invention optimizes the minimization of heat build up during use and facilitates an economical and reliable manufacture of the disk.